Implantable cardiac defibrillators (ICD's) are well known in the art. These devices, encapsulated in a conductive housing or enclosure, are generally implanted in a pectoral region of a patient and electrically connected to the heart with one or more electrode carrying leads. One lead includes at least one defibrillation electrode arranged to be positioned in the right ventricle. An arrhythmia detector detects ventricular arrhythmias, such as ventricular fibrillation. When such an arrhythmia is detected, a pulse generator delivers a defibrillating shock from the defibrillation electrode in the right ventricle to the conductive housing to terminate the arrhythmia. Alternatively, such arrhythmia terminating systems may further include another defibrillation electrode arranged to be positioned in the right atrium and electrically connected to the right ventricular defibrillation electrode. In this arrangement, the defibrillating shock is delivered from the parallel connected right ventricular and right atrial electrodes to the conductive housing.
Ventricular fibrillation is an immediately life threatening cardiac arrhythmia. It requires immediate and effective defibrillation therapy. As a result, when an ICD is implanted within a patient, the implant procedure customarily requires intentional induction of ventricular fibrillation and then immediate defibrillation with the newly implanted device. This is performed to test the device and lead system and to confirm that the device is set and capable to provide a shock voltage that is above the required defibrillation threshold (DFT).
The ventricular fibrillation inductions are carried out in a controlled environment and always with external defibrillation back-up. However, with ventricular fibrillation, there is always a mortality risk associated with the procedure. It would of course be advantageous if such a risk could be avoided.
Modern ICDs generally provide more than a sole defibrillation function. For example, ICDs providing single chamber pacing and/or dual chamber pacing therapy, with or without physiologic rate control, are now customarily implanted. In many cases, a therapy other than defibrillation therapy is the intended primary therapy while defibrillation therapy is secondarily provided and made available because, while the patient has not had a ventricular fibrillation episode, the patient's condition or symptoms indicate a potential for the development of the arrhythmia.
As the functionality of ICDs is further extended, it will become more and more likely that an ICD will be implanted for a primary condition other than ventricular fibrillation. As a result, such devices will be more frequently implanted by physicians who are unwilling to induce ventricular fibrillation during the implant procedure. Hence, it would be most desirable if an ICD were capable of being evaluated and conditioned for providing ventricular fibrillation defibrillation therapy during an implant procedure without the need for ventricular fibrillation induction. It would be further advantageous if such evaluation and conditioning could be performed by the device itself and essentially automatically.